Patent GB-461282-A (GB)
Title: Improvements relating to electron discharge tubes or thermionic valves and circuit arrangements for use therewith
IPC: H03D7/10
Filed: 1935-08-15
Abstract: 461,282. Thermionic valves ; valve circuits for wireless reception. HARRIES, J. H. O. Aug. 15, 1935, No. 23015. [Classes 39 (i) and 40 (v)] A frequency - changer circuit for use in a supersonic heterodyne receiver, has a valve with an anode, a cathode, and at least four grids, one grid being connected as the control grid to a local oscillatory circuit, another to reaction means coupled to that circuit, and a third is connected as a radio-frequency injection grid to the input circuit, the capacity of the oscillation control grid to the radio-frequency injection grid being less than the capacity of the second or reaction grid to the radiofrequency injection grid, so that the latter grid is at a node of potential relative to the potentials on the other two grids, and the oscillating circuit is not coupled with the radio-frequency circuit; the fourth grid may be used for automatic volume control and a fifth as a positive screening grid. The relative values of the capacity are obtained by the positioning and size of the electrodes, and by connecting the first grid to a terminal at the end of the envelope opposite to that at which the other grids are connected; or conducting surfaces may be provided on the grids. As shown in Figs. 1 and 2, an indirectly heated cathode c is surrounded by a grid g<1> of rectangular shape, four grids g<2> . . g<5> formed as circular arcs, and a cylindrical anode a of blackened nickel to prevent secondary emission. The grids are mounted on nickel rods s. Dimensions are given. The mutual conductance of the oscillation-control grid is not less than one milliampere per volt, and of the radio-frequency injection grid not less than 0À25 milliampere per volt. The capacity of its oscillation-control grid to the anode in the absence of the external screen is greater than 0À007 to 0À001 mmfd. The first grid g<1> may give a sharp cut-off, and any of the other grids may give a variable mu characteristic. The lead l<1> to the grid g<1> is taken to a terminal t on the top of the envelope, and the grid g<5> is connected with a side terminal t<5>. A screen e of dished shape with a hollow central portion, is mounted inside the envelope at one end and a hollow screen h at the other end, both screens being connected with the grid g<4>. An external screen s<1> closely surrounds the upper part of the envelope. The anode may be spaced at such a distance from the nearest grid, as described in Specifications 380,429 and 385,968, that the passage of secondary electrons from the anode to that electrode is negligible. Connections for four such valves used in a wireless receiver are shown in Fig. 9, the valve v<1> being a frequency changer, valve v<2> an intermediate frequency amplifier with controlled gain and arranged as a tetrode, v<3> a detector-amplifier, and valve v<4> an output valve. In the valve v<1> the grid g<1> is connected with a tuned oscillatory circuit 1, which is coupled with a reaction coil 2 connected with the grid g<2>. The grid g<3> is connected with the radio-frequency input circuit 3, the grid g<4> with the automatic volume control lead 4, and the grid g<5> through a resistance 5 to a positive potential. The connections to the grids g<3>, g<4> may be interchanged. In the valve v<2> the first grid acts as the input grid, the third as the automatic gain control grid, and the other three grids are connected together and through a resistance 6 to a high tension source so that they act as positive screening grids. In the valve v<3> the anode acts as a diode with the virtual cathode formed between the grids and anode, the first grid acts as the input, the fourth grid as the anode of the amplifier, and the other three grids are connected together as positive screening grids. In the valve v<4>, the first grid is the input grid, the fourth grid is at cathode potential, and the other three grids are positive screening grids connected with a potential divider R<11>, R<12>. In the modified detector-amplifier shown in Fig. 7, the first grid g<1> acts as the input grid, the anode a as a diode, and the output is taken from the other four grids g<2> . . . g<5> connected together. In an output valve connected as a triode, Fig. 8 (not shown), the first grid is the input grid and the other four grids are connected with the anode and the output circuit. Specification 461,310 also is referred to.